In a first conventional example of a charge pump circuit, a flying capacitor is charged with an input voltage, and an output capacitor which is connected to an output terminal is charged with a voltage in which the input voltage is added to the charged voltage in the flying capacitor, and thereby a voltage which is twice the input voltage is produced (see Japanese patent publication number S56-12859). In the case of producing a greater voltage, a voltage of the flying capacitor which is charged with the input voltage is further added to a voltage of the output terminal which is charged to twice the input voltage, and thereby an output voltage which is three times the input voltage is obtained. By repeating the same operation, it is possible to obtain an output voltage which is N times the input voltage.
Additionally, a second conventional example of a charge pump circuit includes a first switching section which produces a voltage, which is the same as an input voltage, in a first capacitor, and a second switching section which produces a voltage, which is smaller than the input voltage, in a second capacitor (see Japanese patent publication number S61-120933). By combining and connecting each of the first and second capacitors and the input voltage, six kinds of output voltages ranging from a voltage which is smaller than the input voltage to a voltage which is greater than the input voltage are produced.
Moreover, in a third conventional example of a charge pump circuit, one flying capacitor outputs an output voltage which is smaller than an input voltage and an output voltage which is greater than the input voltage (see Japanese patent publication number H05-111243).
However, in the first conventional example, an output voltage becomes a voltage which is N times an input voltage, and a voltage which is smaller than the input voltage can not be produced. And additionally, an arbitrary output voltage other than an integral multiple of the input voltage can not be obtained, either. Moreover, in the first conventional example, when an input voltage fluctuates, an output voltage also fluctuates, and no countermeasures are taken for load fluctuations, and therefore an output voltage is unstable.
In the second conventional example, an output voltage which is smaller than an input voltage can be obtained; however a special capacitor is needed, and two capacitors are needed to obtain a voltage which is greater than the input voltage at the same time. Additionally, as well as the first conventional example, in the second conventional example, an arbitrary output voltage can not be obtained, and an output voltage is also unstable in terms of input voltage fluctuations and load fluctuations.
Additionally, in the third conventional example, one flying capacitor is capable of outputting both an output voltage which is greater than an input voltage and an output voltage which is smaller than the input voltage, and it is also possible to change an output voltage by changing an on-duty cycle of a switch section. However, in the third conventional example, it is not possible to change the on-duty cycle of the switch section for each individual output voltage, and therefore an output voltage which can be controlled is limited to one. Moreover, in the third conventional example, a countermeasure for load fluctuations is not taken, and therefore there is a problem in that an output voltage is unstable. Furthermore, an inductor is needed, and therefore it is difficult to achieve a circuit integration.